Electrolyte Regulation in Stabilizing the Interface of a Cobalt-Free Layered Cathode for 4.8 V High-Voltage Lithium-Ion Batteries

The cobalt-free layered oxide cathode of LiNi0.65Mn0.35O2 is promising for high-energy-density lithium-ion batteries (LIBs). However, under high-voltage conditions, severe side reactions between the Co-free cathode and electrolyte, as well as grain boundary cracks and pulverization of particles, hinder its practical applications. Herein, an electrolyte regulation strategy is proposed by adding fluoroethylene carbonate (FEC) and LiPO2F2 as electrolyte additives in carbonate-based electrolytes to address the above issues. As a result, a homogeneous and dense organic-inorganic hybrid cathode electrolyte interface (CEI) film is formed on the cathode surface. The CEI film consists of C-F, LiF, Li2CO3, and LixPOyFz species, which is proven to be highly conductive and effective in suppressing structure damage and alleviating the interfacial reactions between the cathode and electrolyte. With such a CEI film, the interfacial stability of the Co-free cathode and the high-voltage cycling performance of Li||LiNi0.65Mn0.35O2 are greatly improved. A reversible capacity of 155.1 mAh g-1 and a capacity retention of 81.3% over 150 cycles are attained at a 4.8 V charge cutoff voltage with the tamed electrolyte, whereas the cell without the additives only retains 76.1% capacity retention. Therefore, our work demonstrates the synergistic effect of FEC and LiPO2F2 in stabilizing the interface of Co-free cathode materials and provides an alternative strategy for the electrolyte design of high-voltage LIBs.

Improving Fast-Charging Capability of High-Voltage Spinel LiNi0.5 Mn1.5 O4 Cathode under Long-Term Cyclability through Co-Doping Strategy

Co-free spinel LiNi0.5 Mn1.5 O4 (LNMO) is emerging as a promising contender for designing next generation high-energy-density and fast-charging Li-ion batteries, due to its high operating voltage and good Li+ diffusion rate. However, further improvement of the Li+ diffusion ability and simultaneous resolution of Mn dissolution still pose significant challenges for their practical application. To tackle these challenges, a simple co-doping strategy is proposed. Compared to Pure-LNMO, the extended lattice in resulting LNMO-SbF sample provides wider Li+ migration channels, ensuring both enhanced Li+ transport kinetics, and lower energy barrier. Moreover, Sb creating structural pillar and stronger TM─F bond together provides a stabilized spinel structure, which stems from the suppression of detrimental irreversible phase transformation during cycling related to Mn dissolution. Benefiting from the synergistic effect, the LNMO-SbF material exhibits a superior reversible capacity (111.4 mAh g-1 at 5C, and 70.2 mAh g-1 after 450 cycles at 10C) and excellent long-term cycling stability at high current density (69.4% capacity retention at 5C after 1000 cycles). Furthermore, the LNMO-SbF//graphite full cell delivers an exceptional retention rate of 96.9% after 300 cycles, and provides a high energy density at 3C even with a high loading. This work provides valuable insight into the design of fast-charging cathode materials for future high energy density lithium-ion batteries.

Functional Sulfate Additive-Derived Interfacial Layer for Enhanced Electrochemical Stability of PEO-Based Polymer Electrolytes

Solid-state electrolyte batteries have attracted significant interest as promising next-generation batteries due to their achievable high energy densities and nonflammability. In particular, curable polymer network gel electrolytes exhibit superior ion conductivity and interfacial adhesion with electrodes compared to oxide or sulfide solid electrolytes, bringing them closer to commercialization. However, the limited electrochemical stability of matrix polymers, particularly those based on poly (ethylene oxide) (PEO), presents challenges in achieving stable electrochemical performance in high-voltage lithium metal batteries. Here, these studies report a sulfate additive-incorporated thermally crosslinked gel-type polymer electrolyte (SA-TGPE) composed of a PEO-based polymer matrix and a functional sulfate additive, 1,3-propanediolcyclic sulfate (PCS), which forms stable interfacial layers on electrodes. The electrode-electrolyte interface modified by the PCS enhances the electrochemical stability of the polymer electrolyte, effectively alleviating decomposition of the PEO-based polymer matrix on the cathode. Moreover, it also mitigates side reactions of the Ni-rich NCM cathode and dendrites of lithium metal anode. These studies provide a novel perspective by utilizing interfacial modification through electrolyte additives to resolve the electrochemical instability of PEO-based polymer electrolytes in high-voltage lithium metal batteries.

Scalable Precursor-Assisted Synthesis of a High Voltage LiNiyCo1-yPO4 Cathode for Li-Ion Batteries

A solid-solution cathode of LiCoPO4-LiNiPO4 was investigated as a potential candidate for use with the Li4Ti5O12 (LTO) anode in Li-ion batteries. A pre-synthesized nickel-cobalt hydroxide precursor is mixed with lithium and phosphate sources by wet ball milling, which results in the final product, LiNiyCo1-yPO4 (LNCP) by subsequent heat treatment. Crystal structure and morphology of the product were analyzed by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Its XRD patterns show that LNCP is primarily a single-phase compound and has olivine-type XRD patterns similar to its parent compounds, LiCoPO4 and LiNiPO4. Synchrotron X-ray absorption spectroscopy (XAS) analysis, however, indicates that Ni doping in LiCoPO4 is unfavorable because Ni2+ is not actively involved in the electrochemical reaction. Consequently, it reduces the charge storage capability of the LNCP cathode. Additionally, ex situ XRD analysis of cycled electrodes confirms the formation of the electrochemically inactive rock salt-type NiO phase. The discharge capacity of the LNCP cathode is entirely associated with the Co3+/Co2+ redox couple. The electrochemical evaluation demonstrated that the LNCP cathode paired with the LTO anode produced a 3.12 V battery with an energy density of 184 Wh kg-1 based on the cathode mass.

High-Valence Surface-Modified LMO Cathode Materials for Lithium-Ion Batteries: Diffusion Kinetics and Operando Thermal Stability Investigation

Lithium manganese oxide (LiMn2O4) is a prevalent cathode material for lithium-ion batteries due to its low cost, abundant material sources, and ecofriendliness. However, its capacity fade, low energy density, and fast auto-discharge hinders its large-scale commercialization. Consequently, scientists are urged to achieve high-performance LMO cathodes through material doping and surface modification using a wide range of transition metals, polymers, and carbon precursors. Few studies have considered the potential of high-valence transition metal oxides in stabilizing the LMO's cycling process and enhancing the overall battery performance. In this work, we report the synthesis of surface-modified lithium manganese oxide using high-valence tungsten oxide (WVIO3). Different WO3 wt % were investigated before settling for 0.5%WO3-LMO as the synergic surface-modified LMO. Using galvanostatic charge-discharge, 0.50 WO3-LMO exhibited better rate capability by retaining 51% of its initial capacity at a 20C rate, compared to 34% for the pristine LMO. Furthermore, cyclic voltammetry at different scan rates showed that 0.50 WO3-LMO possesses better ion diffusion than pristine LMO, around 10-11 and 10-13 cm2·s-1 respectively. Finally, using in situ Raman spectroscopy, reaction mechanisms during cycling were investigated, and operando accelerating rate calorimetry (ARC) visualized the surface-modified LMO's cycling thermal stability and highlighted its potential use for safe high-voltage lithium-ion batteries in automotive applications.

Sodium Rich Vanadium Oxy-Fluorophosphate - Na3.2 Ni0.2 V1.8 (PO4 )2 F2 O - as Advanced Cathode for Sodium Ion Batteries

Conventional sodium-based layered oxide cathodes are extremely air sensitive and possess poor electrochemical performance along with safety concerns when operating at high voltage. The polyanion phosphate, Na₃ V₂ (PO₄ )₃ stands out as an excellent candidate due to its high nominal voltage, ambient air stability, and long cycle life. The caveat is that Na₃ V₂ (PO₄ )₃ can only exhibit reversible capacities in the range of 100 mAh g^-1 , 20% below its theoretical capacity. Here, the synthesis and characterizations are reported for the first time of the sodium-rich vanadium oxyfluorophosphate, Na_3.2 Ni_0.2 V_1.8 (PO₄ )₂ F₂ O, a tailored derivative compound of Na₃ V₂ (PO₄ )₃ , with extensive electrochemical and structural analyses. Na_3.2 Ni_0.2 V_1.8 (PO₄ )₂ F₂ O delivers an initial reversible capacity of 117 mAh g^-1 between 2.5 and 4.5 V under the 1C rate at room temperature, with 85% capacity retention after 900 cycles. The cycling stability is further improved when the material is cycled at 50 °C within 2.8-4.3 V for 100 cycles. When paired with a presodiated hard carbon, Na_3.2 Ni_0.2 V_1.8 (PO₄ )₂ F₂ O cycled with a capacity retention of 85% after 500 cycles. Cosubstitution of the transition metal and fluorine in Na_3.2 Ni_0.2 V_1.8 (PO₄ )₂ F₂ O as well as the sodium-rich structure are the major factors behind the improvement of specific capacity and cycling stability, which paves the way for this cathode in sodium-ion batteries.

Iron-Vanadium Incorporated Ferrocyanides as Potential Cathode Materials for Application in Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are potential replacements for lithium-ion batteries owing to their comparable energy density and the abundance of sodium. However, the low potential and low stability of their cathode materials have prevented their commercialization. Prussian blue analogs are ideal cathode materials for SIBs owing to the numerous diffusion channels in their 3D structure and their high potential vs. Na/Na⁺. In this study, we fabricated various Fe-V-incorporated hexacyanoferrates, which are Prussian blue analogs, via a one-step synthesis. These compounds changed their colors from blue to green to yellow with increasing amounts of incorporated V ions. The X-ray photoelectron spectroscopy spectrum revealed that V³⁺ was oxidized to V⁴⁺ in the cubic Prussian blue structure, which enhanced the electrochemical stability and increased the voltage platform. The vanadium ferrocyanide Prussian blue (VFPB1) electrode, which contains V⁴⁺ and Fe²⁺ in the Prussian blue structure, showed Na insertion/extraction potential of 3.26/3.65 V vs. Na/Na⁺. The cycling test revealed a stable capacity of ~70 mAh g^-1 at a rate of 50 mA g^-1 and a capacity retention of 82.5% after 100 cycles. We believe that this Fe-V-incorporated Prussian green cathode material is a promising candidate for stable and high-voltage cathodes for SIBs.

Study of a High-Voltage NMC Interphase in the Presence of a Thiophene Additive Realized by Operando SHINERS

Improving the electrochemical properties and cycle life of high-voltage cathodes in lithium-ion batteries requires a deep understanding of the structural properties and failure mechanisms at the cathode electrolyte interphase (CEI). We present a study implementing an advanced Raman spectroscopy technique to specifically address the compositional features of interphase during cell operation. Our operando technique, shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), provides a reliable platform to investigate the dynamics of the interphase structure and elucidate the compositional changes near the cathode surface. To improve the CEI properties, thiophene was introduced and investigated as an effective, high-voltage film-forming additive by largely diminishing the capacity fading triggered at high potentials in LiNi_1/3Co_1/3Mn_1/3O₂ cathodes. While the cells without thiophene show severe capacity fading, cells with an optimized concentration of thiophene exhibit a significant performance improvement. Operando SHINERS detects the presence of a stable CEI. The results suggest that the composition of the CEI is dominated by polythiophene and copolymerization products of ethylene carbonate with thiophene, which protects the electrolyte components from further decomposition. The formation mechanism of the polymeric film was modeled using quantum chemistry calculations, which shows good agreement with the experimental data.

Styrene-Based Poly(ethylene oxide) Side-Chain Block Copolymers as Solid Polymer Electrolytes for High-Voltage Lithium-Metal Batteries

Herein, we report the design of styrene-based poly(ethylene oxide) (PEO) side-chain block copolymers featuring a microphase separation and their application as solid polymer electrolytes in high-voltage lithium-metal batteries. A straightforward synthesis was established, overcoming typical drawbacks of PEO block copolymers prepared by anionic polymerization or ester-based PEO side-chain copolymers. Both the PEO side-chain length and the LiTFSI content were varied, and the underlying relationships were elucidated in view of polymer compositions with high ionic conductivity. Subsequently, a selected composition was subjected to further analyses, including phase-separated morphology, providing not only excellent self-standing films with intrinsic mechanical stability but also the ability to suppress lithium dendrite growth as well as good flexibility, wettability, and good contacts with the electrodes. Furthermore, good thermal and electrochemical stability was demonstrated. To do so, linear sweep and cyclic voltammetry, lithium plating/stripping tests, and galvanostatic overcharging using high-voltage cathodes were conducted, demonstrating stable lithium-metal interfaces and a high oxidative stability of around 4.75 V. Consequently, cycling of Li||NMC622 cells did not exhibit commonly observed rapid cell failure or voltage noise associated with PEO-based electrolytes in Li||NMC622 cells, attributed to the high mechanical stability. A comprehensive view is provided, highlighting that the combination of PEO and high-voltage cathodes is not impossible per se.

Double-Layered Multifunctional Composite Electrolytes for High-Voltage Solid-State Lithium-Metal Batteries

The need for safe storage systems with a high energy density has increased the interest in high-voltage solid-state Li-metal batteries (LMBs). Solid-state electrolytes, as a key material for LMBs, must be stable against both high-voltage cathodes and Li anodes. However, the weak interfacial contact between the electrolytes and electrodes poses challenges in the practical applications of LMBs. In this study, a double-layered solid composite electrolyte (DLSCE) was synthesized by introducing an antioxidative poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP)-10 wt % Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) to the cathode interface, whereas a lithium-friendly poly(oxyethylene) (PEO)-5 wt % LATP was made to come into contact with Li metal. Owing to the heterogeneous double-layered structure of the DLSCE, a high ionic transfer number (0.43), high ionic conductivity (1.49 × 10^-4 S/cm), and a wide redox window (4.82 V) were obtained at ambient temperature. Moreover, the DLSCE showed excellent Li-metal stability, thereby enabling the Li-Li symmetric cells to stably run for over 600 h at 0.2 mA/cm² with effective lithium dendrite inhibition. When paired with a high-voltage LiNi_1/3Co_1/3Mn_1/3O₂ cathode, the Li/DLSCE/NCM111 cell exhibited excellent electrochemical performance: long-term cyclability with 85% capacity retention could be conducted at 0.2C after 100 cycles corresponding to 100% Coulombic efficiencies.

A General Strategy of Anion-Rich High-Concentration Polymeric Interlayer for High-Voltage, All-Solid-State Batteries

All-solid-state batteries are promising energy storage systems as a power source for future electric applications. However, the solid electrolytes have suffered from oxidative vulnerability at the catalytic cathode's surface, particularly at the high-voltage charging process. The poor charge transport and the contact issue at the electrolyte/electrode interface also hamper fully utilizing high-energy-density batteries. In this work, a general design of a high-concentration polymeric interlayer is developed. The interactions between a number of anions in the high-salt-concentration and the polymer chain's functional groups have shown outstanding physicochemical properties, including the rich solvation sites and conductive nanochannels, which Li⁺ ions can coordinate to or conduct through. The high-concentration polymeric interlayer is also highly resistant to oxidation (up to 5 V) that leads to significant improvement in cycle life with various cathodes, including LiNi_1/3Co_1/3Mn_1/3O₂, LiCoO₂ and LiFePO₄, demonstrating a high Coulombic efficiency over 99.9%.

Electrosprayed Robust Graphene Layer Constructing Ultrastable Electrode Interface for High-Voltage Lithium-Ion Batteries

Aluminum (Al) foil serving as the most widely used cathode current collector for lithium-ion batteries (LIBs) is still not flawless to fulfill the increasing demand of rechargeable energy storage systems. The limited contact area and weak adhesion to cathode material as well as local corrosion during long-term operations could deteriorate the performance of LIBs with a higher working voltage. Herein, a reduced graphene oxide (RGO)-modified Al foil (RGO/Al) is developed via electrospraying to increase interfacial adhesion and inhibit anodic corrosion as a functional current collector. Valid corrosion resistance to electrolyte and strengthened adhesion of electrode particles to current collectors are beneficial to improve the interfacial reaction dynamics. The RGO/Al-based LiNi_0.5Mn_1.5O₄ cells (LNMO-RGO/Al) exhibit better electrochemical performances in terms of long-term cycling discharge capacity retention (90% after 840 cycles at 1 C), rate capability (101.8 mAh g^-1 at 5 C), and interfacial resistance, prominently superior to bare Al-based cells (LNMO-Al). This work not only contributes to long-term stable operation of high-voltage LIBs but also brings new opportunities for the development of next-generation 5 V LIBs.

Stabilized High-Voltage Cathodes via an F-Rich and Si-Containing Electrolyte Additive

High-voltage cathodes provide a promising solution to the energy density limitation of currently commercialized lithium-ion batteries, but they are unstable in electrolytes during the charge/discharge process. To address this issue, we propose a novel electrolyte additive, pentafluorophenyltriethoxysilane (TPS), which is rich in elemental F and contains elemental Si. The effectiveness of TPS has been demonstrated by cycling a representative high-voltage cathode, LiNi_0.5Mn_1.5O₄ (LNMO), in 1.0 M LiPF₆-diethyl carbonate/ethylene carbonate/ethyl methyl carbonate (2/3/5 in weight). LNMO presents an increased capacity retention from 28 to 85% after 400 cycles at 1 C by applying 1 wt % TPS. Further electrochemical measurements combined with spectroscopic characterization and theoretical calculations indicate that TPS can not only construct a robust protective cathode electrolyte interphase via its oxidation during initial lithium desertion but also scavenge the detrimental hydrogen fluoride (HF) present in the electrolyte via its strong combination with the species HF, F^-, and H⁺, highly stabilizing LNMO during the charge/discharge process. These features of TPS provide a new solution to the obstacle in the practical application of high-voltage cathodes not limited to LNMO.

Revisiting the Stability of the Cr4+/Cr3+ Redox Couple in Sodium Superionic Conductor Compounds

In this work, we revisited the stability of the Cr⁴⁺/Cr³⁺ redox couple in a sodium superionic conductor (NASICON)-type compound, Na₂TiCr(PO₄)₃. Experimental results showed that the Na₂TiCr(PO₄)₃ compound exhibited a specific capacity of 49.9 mA h g^-1 at 20 mA g^-1, about 80% of its theoretical capacity of 62.2 mA h g^-1 with one Na⁺ insertion/deinsertion per formula Na₂TiCr(PO₄)₃. The redox couple was found to be stable against cycling with some 90.3% capacity retention after 300 cycles within the voltage range between 2.5 and 4.7 V. With a wider voltage range between 2.5 and 5.0 V, the capacity retention was about 76.6% after 1000 cycles, indicating the redox couple is stable against overvoltage. In addition, the effect of Ti/Cr ratio on the reversibility of the redox couple was studied by varying x in Na_1+xTi_2-xCr_x(PO₄)₃ (where x = 0.6, 0.8, 1.0, 1.2, 1.4, 2.0). It was confirmed that x = 1 is optimal for balancing the electrode stability and the capacity. The obtained optimal content of Cr in the compound provides useful guidance for designing new Cr-based NASICON-type cathode materials. Furthermore, in situ X-ray diffraction (XRD) analysis of compound Na₂TiCr(PO₄)₃ indicated a two-phase sodium-ion storage mechanism, which is different from the previously reported one-phase mechanism. Rietveld refinement XRD analysis showed a small volume change of the compound during cycling (about 2.6%), indicating good structural stability.

Stable Cycling of High-Voltage Lithium-Metal Batteries Enabled by High-Concentration FEC-Based Electrolyte

Functional electrolytes that are stable toward both Li-metal anode and high-voltage (>4 V vs Li/Li⁺) cathodes play a critical role in the development of high-energy density Li-metal batteries. Traditional carbonate-based electrolytes can hardly be used in high-voltage Li-metal batteries due to the dendritic Li deposits, low Coulombic efficiency, and anodic instability in the presence of aggressive cathodes. Herein, we design a concentrated dual-salt electrolyte that achieves high stability for both Li anodes and high-voltage cathodes of LiNi_0.5Mn_1.5O₄ (LNMO) and LiNi_0.7Co_0.15Mn_0.15O₂ (NCM). A Li||Cu cell in the designed electrolyte shows a high Coulombic efficiency of >98% in long-term plating/stripping for 900 cycles. Li||LNMO and Li||NCM cells achieve a capacity retention of 88.5% over 500 cycles and 86.2% over 200 cycles with a cutoff voltage of 4.9 and 4.3 V, respectively. The Li||LNMO full cell with a cathode areal capacity of 1.8 mAh/cm² and only 3× excess Li was fabricated, and it delivered a high capacity retention of 87.8% after 100 cycles. The reasons for the good cycling stability of the cells in a concentrated dual-salt electrolyte can be attributed to the reversible dendrite-free plating/stripping of a Li-metal anode and stable interfacial layers on both anode and cathode.

Carbon Nanotubes Coupled with Metal Ion Diffusion Layers Stabilize Oxide Conversion Reactions in High-Voltage Lithium-Ion Batteries

Creating new architectures combined with super diverse materials for achieving more excellent performances has attracted great attention recently. Herein, we introduce a novel dual metal (oxide) microsphere reinforced by vertically aligned carbon nanotubes (CNTs) and covered with a titanium oxide metal ion-transfer diffusion layer. The CNTs penetrate the oxide particles and buffer structural volume change while enhancing electrical conductivity. Meanwhile, the external TiO₂-C shell serves as a transport pathway for mobile metal ions (e.g., Li⁺) and acts as a protective layer for the inner oxides by reducing the electrolyte/metal oxide interfacial area and minimizing side reactions. The proposed design is shown to significantly improve the stability and Coulombic efficiency (CE) of metal (oxide) anodes. For example, the as-prepared MnO-CNTs@TiO₂-C microsphere demonstrates an extremely high capacity of 967 mA h g^-1 after 200 cycles, where a CE as high as 99% is maintained. Even at a harsh rate of 5 A g^-1 (ca. 5 C), a capacity of 389 mA h g^-1 can be maintained for thousands of cycles. The proposed oxide anode design was combined with a nickel-rich cathode to make a full-cell battery that works at high voltage and exhibits impressive stability and life span.

Stable Thiophosphate-Based All-Solid-State Lithium Batteries through Conformally Interfacial Nanocoating

All-solid-state lithium batteries (ASLBs) are promising for the next generation energy storage system with critical safety. Among various candidates, thiophosphate-based electrolytes have shown great promise because of their high ionic conductivity. However, the narrow operation voltage and poor compatibility with high voltage cathode materials impede their application in the development of high energy ASLBs. In this work, we studied the failure mechanism of Li₆PS₅Cl at high voltage through in situ Raman spectra and investigated the stability with high-voltage LiNi_1/3Mn_1/3Co_1/3O₂ (NMC) cathode. With a facile wet chemical approach, we coated a thin layer of amorphous Li_0.35La_0.5Sr_0.05TiO₃ (LLSTO) with 15-20 nm at the interface between NMC and Li₆PS₅Cl. We studied different coating parameters and optimized the coating thickness of the interface layers. Meanwhile, we studied the effect of NMC dimension to the ASLBs performance. We further conducted the first-principles thermodynamic calculations to understand the electrochemical stability between Li₆PS₅Cl and carbon, NMC, LLSTO, NMC/LLSTO. Attributed to the high stability of Li₆PS₅Cl with NMC/LLSTO and outstanding ionic conductivity of the LLSTO and Li₆PS₅Cl, at room temperature, the ASLBs exhibit outstanding capacity of 107 mAh g^-1 and keep stable for 850 cycles with a high capacity retention of 91.5% at C/3 and voltage window 2.5-4.0 V (vs Li-In).

Dioxolanone-Anchored Poly(allyl ether)-Based Cross-Linked Dual-Salt Polymer Electrolytes for High-Voltage Lithium Metal Batteries

Novel cross-linked polymer electrolytes (XPEs) are synthesized by free-radical copolymerization induced by ultraviolet (UV)-light irradiation of a reactive solution, which is composed of a difunctional poly(ethylene glycol) diallyl ether oligomer (PEGDAE), a monofunctional reactive diluent 4-vinyl-1,3-dioxolan-2-one (VEC), and a stock solution containing lithium salt (lithium bis(trifluoromethanesulfonyl)imide, LiTFSI) in a carbonate-free nonvolatile plasticizer, poly(ethylene glycol) dimethyl ether (PEGDME). The resulting polymer matrix can be represented as a linear polyethylene chain functionalized with cyclic carbonate (dioxolanone) moieties and cross-linked by ethylene oxide units. A series of XPEs are prepared by varying the [O]/[Li] ratio (24 to 3) of the stock solution and thoroughly characterized using physicochemical (thermogravimetric analysis-mass spectrometry, differential scanning calorimetry, NMR, etc.) and electrochemical techniques. In addition, quantum chemical calculations are performed to elucidate the correlation between the electrochemical oxidation potential and the lithium ion-ethylene oxide coordination in the stock solution. Later, lithium bis(fluorosulfonyl)imide (LiFSI) salt is incorporated into the electrolyte system to produce a dual-salt XPE that exhibits improved electrochemical performance, a stable interface against lithium metal, and enhanced physical and chemical characteristics to be employed against high-voltage cathodes. The XPE membranes demonstrated excellent resistance against lithium dendrite growth even after reversibly plating and stripping lithium ions for more than 1000 h with a total capacity of 0.5 mAh cm^-2. Finally, the XPE films are assembled in a lab-scale lithium metal battery configuration by using carbon-coated LiFePO₄ (LFP) or LiNi_0.8Co_0.15Al_0.05O₂ (NCA) as a cathode and galvanostatically cycled at 20, 40, and 60 °C. Remarkably, at 20 °C, the NCA-based lithium metal cells displayed excellent cycling stability and good capacity retention (>50%) even after 1000 cycles.

Biofilm Nanofiber-Coated Separators for Dendrite-Free Lithium Metal Anode and Ultrahigh-Rate Lithium Batteries

Rechargeable batteries that combine high energy density with high power density are highly demanded. However, the wide utilization of lithium metal anode is limited by the uncontrollable dendrite growth, and the conventional lithium-ion batteries (LIBs) commonly suffer from low rate capability. Here, we for the first time develop a biofilm-coated separator for high-energy and high-power batteries. It reveals that the coating of Escherichia coli protein nanofibers can improve electrolyte wettability and lithium transference number and enhance adhesion between separators and electrodes. Thus, lithium dendrite growth is impeded because of the uniform distribution of the Li-ion flux. The modified separator also enables the stable cycling of high-voltage Li|Li_1.2Mn_0.6Ni_0.2O₂ (LNMO) cells at an extremely high rate of 20 C, delivering a high specific capacity of 83.1 mA h g^-1, which exceeds the conventional counterpart. In addition, the modified separator in the Li₄Ti₅O₁₂|LNMO full cell also exhibits a larger capacity of 68.2 mA h g^-1 at 10 C than the uncoated separator of 37.4 mA h g^-1. Such remarkable performances of the modified separators arise from the conformal, adhesive, and endurable coating of biofilm nanofibers. Our work opens up a new opportunity for protein-based biomaterials in practical application of high-energy and high-power batteries.

High-performance all-solid-state batteries enabled by salt bonding to perovskite in poly(ethylene oxide)

Flexible and low-cost poly(ethylene oxide) (PEO)-based electrolytes are promising for all-solid-state Li-metal batteries because of their compatibility with a metallic lithium anode. However, the low room-temperature Li-ion conductivity of PEO solid electrolytes and severe lithium-dendrite growth limit their application in high-energy Li-metal batteries. Here we prepared a PEO/perovskite Li_3/8Sr_7/16Ta_3/4Zr_1/4O₃ composite electrolyte with a Li-ion conductivity of 5.4 × 10^-5 and 3.5 × 10^-4 S cm^-1 at 25 and 45 °C, respectively; the strong interaction between the F^- of TFSI^- (bis-trifluoromethanesulfonimide) and the surface Ta⁵⁺ of the perovskite improves the Li-ion transport at the PEO/perovskite interface. A symmetric Li/composite electrolyte/Li cell shows an excellent cyclability at a high current density up to 0.6 mA cm^-2 A solid electrolyte interphase layer formed in situ between the metallic lithium anode and the composite electrolyte suppresses lithium-dendrite formation and growth. All-solid-state Li|LiFePO₄ and high-voltage Li|LiNi_0.8Mn_0.1Co_0.1O₂ batteries with the composite electrolyte have an impressive performance with high Coulombic efficiencies, small overpotentials, and good cycling stability.

Li-Rich Li[Li1/6 Fe1/6 Ni1/6 Mn1/2 ]O2 (LFNMO) Cathodes: Atomic Scale Insight on the Mechanisms of Cycling Decay and of the Improvement due to Cobalt Phosphate Surface Modification

Lithium-rich Li[Li_1/6 Fe_1/6 Ni_1/6 Mn_1/2 ]O₂ (0.4Li₂ MnO₃ -0.6LiFe_1/3 Ni_1/3 Mn_1/3 O₂ , LFNMO) is a new member of the xLi₂ MnO₃ ·(1 - x)LiMO₂ family of high capacity-high voltage lithium-ion battery (LIB) cathodes. Unfortunately, it suffers from the severe degradation during cycling both in terms of reversible capacity and operating voltage. Here, the corresponding degradation occurring in LFNMO at an atomic scale has been documented for the first time, using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), as well as tracing the elemental crossover to the Li metal anode using X-ray photoelectron spectroscopy (XPS). It is also demonstrated that a cobalt phosphate surface treatment significantly boosts LFNMO cycling stability and rate capability. Due to cycling, the unmodified LFNMO undergoes extensive elemental dissolution (especially Mn) and O loss, forming Kirkendall-type voids. The associated structural degradation is from the as-synthesized R-3m layered structure to a disordered rock-salt phase. Prior to cycling, the cobalt phosphate coating is epitaxial, sharing the crystallography of the parent material. During cycling, a 2-3 nm thick disordered Co-rich rock-salt structure is formed as the outer shell, while the bulk material retains R-3m crystallography. These combined cathode-anode findings significantly advance the microstructural design principles for next-generation Li-rich cathode materials and coatings.

New Spin on Organic Radical Batteries-An Isoindoline Nitroxide-Based High-Voltage Cathode Material

Organic electrode materials are a highly promising and environmentally benign class of battery materials with radical polymers being at the forefront of this research. Herein, we report the first example of the 1,1,3,3-tetramethylisoindolin-2-yloxyl class of nitroxides as an organic electrode material and the synthesis and application of a novel styrenic nitroxide polymer, poly(5-vinyl-1,1,3,3-tetramethylisoindolin-2-yloxyl) (PVTMIO). The polymer was synthesized from the precursor monomer, 2-methoxy-5-vinyl-1,1,3,3-tetramethylisoindoline, and subsequent oxidative deprotection yielded the electroactive radical species. Cyclic voltammetry revealed a high oxidation potential of 3.7 V versus Li, placing it among the top of the nitroxide class of electrode materials. The suitability of PVTMIO for utilization in a high-voltage organic radical battery was confirmed with a discharge capacity of 104.7 mAh g^-1, high rate performance, and stability under cycling conditions (90% capacity retention after 100 cycles), making it one of the highest reported organic p-dopable cathode materials.

Complementary Strategies Toward the Aqueous Processing of High-Voltage LiNi0.5 Mn1.5 O4 Lithium-Ion Cathodes

Increasing the environmental benignity of lithium-ion batteries is one of the greatest challenges for their large-scale deployment. Toward this end, we present herein a strategy to enable the aqueous processing of high-voltage LiNi_0.5 Mn_1.5 O₄ (LNMO) cathodes, which are considered highly, if not the most, promising for the realization of cobalt-free next-generation lithium-ion cathodes. Combining the addition of phosphoric acid with the cross-linking of sodium carboxymethyl cellulose by means of citric acid, aqueously processed electrodes with excellent performance are produced. The combined approach offers synergistic benefits, resulting in stable cycling performance and excellent coulombic efficiency (98.96 %) in lithium-metal cells. Remarkably, this approach can be easily incorporated into standard electrode preparation processes with no additional processing step.

Impact of Cl Doping on Electrochemical Performance in Orthosilicate (Li2FeSiO4): A Density Functional Theory Supported Experimental Approach

Safe and high-capacity cathode materials are a long quest for commercial lithium-ion battery development. Among various searched cathode materials, Li₂FeSiO₄ has taken the attention due to optimal working voltage, high elemental abundance, and low toxicity. However, as per our understanding and observation, the electrochemical performance of this material is significantly limited by the intrinsic low electronic conductivity and slow lithium-ion diffusion, which limits the practical capacity (a theoretical value of ∼330 mAh g^-1). In this report, using first-principles density functional theory based approach, we demonstrate that chlorine doping on oxygen site can enhance the electronic conductivity of the electrode and concurrently improve the electrochemical performance. Experimentally, X-ray diffraction, X-ray photoelectron spectroscopy, and field-emission gun scanning electron microscopy elemental mapping confirms Cl doping in Li_2-xFeSiO_4-xCl_x/C (x ≤ 0.1), while electrochemical cycling performance demonstrated improved performance. The theoretical and experimental studies collectively predict that, via Cl doping, the lithium deinsertion voltage associated with the Fe²⁺/Fe³⁺ and Fe³⁺/Fe⁴⁺ redox couples can be reduced and electronic conductivity can be enhanced, which opens up the possibility of utilization of silicate-based cathode with carbonate-based commercial electrolyte. In view of potential and electronic conductivity benefits, our results indicate that Cl doping can be a promising low-cost method to improve the electrochemical performance of silicate-based cathode materials.

Graphite//LiNi0.5 Mn1.5 O4 Cells Based on Environmentally Friendly Made-in-Water Electrodes

The performance of graphite//LiNi_0.5 Mn_1.5 O₄ (LNMO) cells, both electrodes of which are made using water-soluble sodium carboxymethyl cellulose (CMC) binder, is reported for the first time. The full cell performed outstandingly over 400 cycles in the conventional electrolyte ethylene carbonate/dimethyl carbonate-1 m LiPF₆ , and the delivered specific energy at the 100th, 200th, 300th, and 400th cycle corresponded to 82, 78, 73, and 66 %, respectively, of the initial energy value of 259 Wh kg^-1 (referring to the sum of the two electrode-composite weights). The good stability of high-voltage, LNMO-CMC-based electrodes upon long-term cycling is discussed and the results are compared to those of LNMO-composite electrodes with polyvinylidene fluoride (PVdF). LNMO-CMC electrodes outperformed those with PVdF binder, displaying a capacity retention of 83 % compared to 62 % for the PVdF-based electrodes after 400 cycles at 1 C. CMC promotes a more compact and stable electrode surface than PVdF; undesired interfacial reactions at high operating voltages are mitigated, and the thickness of the passivation layer on the LNMO surface is reduced, thereby enhancing its cycling stability.

Combining Optimized Particle Morphology with a Niobium-Based Coating for Long Cycling-Life, High-Voltage Lithium-Ion Batteries

Morphologically optimized LiNi0.5 Mn1.5 O4 (LMNO-0) particles were treated with LiNbO3 to prepare a homogeneously coated material (LMNO-Nb) as cathode in batteries. Graphite/LMNO-Nb full cells present a twofold higher cycling life than cells assembled using uncoated LMNO-0 (graphite/LMNO-0 cell): Graphite/LMNO-0 cells achieve 80 % of the initial capacity after more than 300 cycles whereas for graphite/LMNO-Nb cells this is the case for more than 600 cycles. Impedance spectroscopy measurements reveal significantly lower film and charge-transfer resistances for graphite/LMNO-Nb cells than for graphite/LMNO-0 cells during cycling. Reduced resistances suggest slower aging related to film thickening and increase of charge-transfer resistances when using LMNO-Nb cathodes. Tests at 45 °C confirm the good electrochemical performance of the investigated graphite/LMNO cells while the cycling stability of full cells is considerably lowered under these conditions.

Improving the High-Voltage Li2FeMn3O8 Cathode by Chlorine Doping

High-capacity and high-voltage cathode materials are desirable for high-energy-density lithium ion batteries. Among various cathode materials, Li2FeMn3O8 is attractive due to its high working voltage, low toxicity, and low cost. However, its superior electrochemical properties are significantly limited by the intrinsic defects in the Li2FeMn3O8 cathode, which makes the theoretical working voltage (4.9 V) and capacity (148 mAh/g) hard to reach. In this paper, we demonstrated that Cl doping can effectively increase the capacity and working voltage of the Li2FeMn3O8 cathode. X-ray photoelectron spectroscopy reveals that Cl doping reduced the valence state and increased the electron binding energy in cations and thus increased the voltage and enhanced the capacity of the Li2FeMn3O8 cathode. Our results also indicate that Cl doping can be a promising low-cost method to improve the electrochemical performance of various oxide cathode materials, including LiCoO2 and LiMn2O4.

Sol-gel synthesis of aliovalent vanadium-doped LiNi(0.5)Mn(1.5)O(4) cathodes with excellent performance at high temperatures

Extraordinary performance at elevated temperature is achieved for high-voltage spinel-phase LiNi0.5 Mn1.5 O4 cathodes prepared using an adipic-acid-assisted sol-gel technique and doped with vanadium. V-substitution in the Li sites (Wykoff position 8a) is confirmed by V K-edge X-ray absorption spectroscopy and Rietveld refinement (Li0.995 V0.005 Ni0.5 Mn1.5 O4 ). V-doped LiNi0.5 Mn1.5 O4 delivered a reversible capacity of approximately 130 and 142 mAh g(-1) at ambient and elevated temperature conditions, respectively. Furthermore, the Li0.995 V0.005 Ni0.5 Mn1.5 O4 phase rendered approximately 94 % and 84 % of initial capacity compared to approximately 85 % and 3 % for the LiNi0.5 Mn1.5 O4 phase after 100 cycles in ambient and elevated temperature conditions, respectively. The enhancements are mainly because of the suppression of Mn dissolution and unwanted side reaction with electrolyte counterpart, and to the increase in conductivity, improving the electrochemical profiles for the V-doped phase.